﻿using System;

namespace FpAgain.OOP {
  
abstract class Tree {
  public class Sum : Tree {
    public mutable l : Tree;
    public mutable r : Tree;
  }
  
  public class Sin : Tree {
    public mutable op : Tree;
  }
  
  public class Variable : Tree {
    public mutable name : string;
  }
}

}